SPOKANE, Wash. (AP) -- Forgotten amid all that angst over Purdue's NCAA tournament chances without Robbie Hummel: The Boilermakers still have Keaton Grant.

The senior, who became a starter after the do-it-all Hummel blew out his knee three weeks ago, ignited a decisive, 20-3 run with 11 points to begin the second half. That opened up the inside for teammate JuJuan Johnson's 23 points and rallied fourth-seeded Purdue past No. 13 seed Siena 72-64 on Friday in the first round of the South Regional.

Johnson, the tallest player on either team at 6-foot-10, tied his career high with 15 rebounds.

E'Twaun Moore added 12 points for the Boilermakers (28-5). They were steamed that even President Barack Obama had joined a national chorus predicting the Saints (27-7) would pull a first-round upset in the third consecutive NCAA tournament.

Take that, Mr. President!

Edwin Ubiles scored 18 points for Siena, which came from 15 points down to pull within 66-63 on a layup by Ryan Rossiter off a deft pass by Ronald Moore with 62 seconds left--before Purdue clinched the win with free throws.

Then Lewis Jackson, who had airballed a shot and missed a free throw seconds earlier, made two foul shots. The first, tension-breaking one plopped in after a thud onto the back rim as Jackson sheepishly smiled.

Ronald Moore missed from inside off the front rim at the other end with 40 seconds remaining, and Chris Kramer made two foul shots to put Purdue up 70-63 with 33.9 seconds left. Then Johnson added two free throws with 28.6 seconds to go to make it 72-64.

The small school with 3,000 undergraduates outside Albany, N.Y., had beaten Ohio State and Vanderbilt to begin its previous two NCAA tournaments--and talked Thursday of even feeling pressure as a "favored" No. 13 seed.

Purdue's win after a 3-2 stretch without Hummel left No. 13 seeds just 22-80 in games against No. 4 seeds since the tournament expanded to 64 teams in 1985. They added another loss when Wisconsin held off Wofford later in the day.

Purdue's early decision-making on offense--freshman point guard Kelsey Barlow's pass into Siena's zone to no one, a full-court pass over the head of towering Johnson and into the Siena band--had coach Matt Painter sitting on the scorer's table near his bench and yelling, "What are we doing?"

He knew after halftime.

The Boilermakers charged out of the locker room to score the first 13 points.

Purdue had missed eight of its first nine 3-point shots before going 3 for 4 to start the second half. Grant had all three of those, after missing his first four shots. That shooting opened up the inside, and Johnson roamed free for dunks over the bewildered Saints.

Grant's first 3-pointer changed the tone of the game. And when Lewis Jackson, playing with a foot fracture, zoomed uncontested down the lane for a scoop shot, Purdue had instantly turned a three-point deficit into a 37-32 lead.

Siena called timeout, and frustrated Saints coach Fran McCaffery got a bench warning for being on the court and yelling.

As McCaffery swore at his players throughout the timeout, his players felt their own warning--that their third consecutive first-round upset in the NCAAs was slipping away.

Grant hit another 3 after the timeout, and Chris Kramer stole the ball at halfcourt, soared for a breakaway dunk and yelled to his teammates on the bench. Purdue led 42-32 with 17 minutes left, and McCaffery glared at the officials to begin his second timeout.

When Grant made his third consecutive 3, from the wing, former Boilermakers coach Gene Keady was on his feet two rows behind the Purdue bench and roaring over the 45-35 lead.

Siena's best answer from 3-point range was on the bench. Starter Clarence Jackson, a 39-percent shooter from deep, did not play after spraining his ankle.